Embodiments of the inventive concept relate generally to optical modulators. More particularly, embodiments of the inventive concept relate to optical modulators formed on a bulk-silicon substrate.
Traditionally, electrical and optical components of electronic devices have been fabricated separately and then connected to each other on a printed circuit board (PCB). These separate fabrication processes, however, tend to drive up the cost of the electronic devices. Accordingly, recent efforts have been dedicated to incorporating optical and electrical components into a single integrated circuit (IC). An IC comprising optical components can be referred to as an optical IC.
The optical components in an optical IC can be roughly classified as active devices and passive devices. Active devices are devices supplied with power, such as a light source, an optical modulator, or an optical receiver. Passive devices are devices not supplied with power, such as a waveguide, a coupler, an optical filter, or a multiplexer.
Optical modulators can be further classified into interferometer-type and resonant-type optical modulators. Interferometer-type optical modulators typically operate at high speeds, have a broad operating spectrum band, and are stable in the presence of temperature changes. However, interferometer-type optical modulators are relatively large compared to resonant-type optical modulators. Resonant-type optical modulators are generally smaller than interferometer-type optical modulators, but they typically have a narrower operating spectrum band and are more sensitive to temperature changes.
Optical modulators are commonly formed in a silicon-on-insulator (SOI) substrate, with a waveguide formed by a high refractive index silicon core surrounded by a low refractive index cladding layer. A buried oxide (BOX) of the SOI substrate can be used to form a bottom portion of the cladding layer. This can simplify the process of manufacturing the waveguide. Unfortunately, however, the SOI substrate is significantly more expensive than other types of substrates, such as a bulk-silicon (bulk-Si) substrate.